Sealing mechanisms for storage tanks



March 7, 1967 w, DE BOCK SEALING MECHANISMS FOR STORAGE TANKS 2 Sheets-Sheet 1 Filed Feb. 12, 1965 lN VEN TOR WALTER L. DE BOCK ATTYS.

March 7, 1967 W. L. DE BOCK SEALING MECHANISMS FOR STORAGE TANKS 2 Sheets-Sheet 2 Filed Feb. 12, 1965 United States Patent 3,307,733 SEALING MECHANISMS FUR STORAGE TANKS Walter L. De Bock, Riverdaie, Ill., assignor to General American Transportation Corporation, Chicago, Ill., a corporation of Illinois Filed Feb. 12, 1965, Ser. No. 432,303 2 Claims. (Cl. 22026) The present invention relates to scaling mechanisms for storage tanks for petroleum products, or the like, and more particularly to such a sealing mechanism for such a tank of the type having an upstanding substantially cylindrical side wall and provided with a floating roof carrying the sealing mechanism with it arranged in sliding sealing engagement with the side wall, thereby to minimize evaporation of the stored petroleum products, to reduce the fire hazard involved and to protect the petroleum products from the elements of weather; and it is a general object of the invention to provide an improved sealing mechanism of the general type of that disclosed in U.S. Patent No. 3,043,468, granted on JulylO, 1962, to Frank W. H-orner, Jr.

Another object of the invention is to provide sealing mechanism of the type noted that comprises a substantially annular tubular casing carried by the upper portion of the roof wall structure in surrounding relation therewith and positioned in the annular space defined between the roof wall structure and the tank side Wall and movable with the roof wall structure and maintain-ed in sealing engagement with the tank side wall notwithstanding both vertical and sidewise movements of the roof wall structure relative to the tank side wall and that is of economical construction and arrangement and that may be installed upon the floating roof in a simple and ready manner.

Another object of the invention is to provide sealing mechanism of the construction described, and further comprising an annular body of self-supporting resilient material of cellular structure enclosed by the casing and substantially completely filling the casing, so that the casing constitutes an outer wrapper for the body, and so that the body constitutes a resilient cushion urging the casing into firm sealed relation with both the adjacent roof wall structure and the adjacent tank side wall.

A further object of the invention is to provide sealing mechanism of the construction described, and further comprising a plurality of stays carried by the roof wall structure in an annular array and positioned in circumferentially spaced-apart relation with respect to each other, wherein the stays are secured to the upper portion of the roof Wall structure above the casing and project downwardly along the roof wall structure and into the casing and between the inner side wall of the casing and the adjacent inner side of the body, and wherein the stays respectively terminate at the lower portions thereof in parts located adjacent to the junction between the lower portion of the casing inner side wall and the outer portion of the casing bottom wall, whereby the stays positively prevent the casing from riding-up the tank side wall and out of the annular space incident to downward movement of the roof wall structure with respect to the tank side wall.

A still further object of the invention is to provide sealing mechanism of the character described, and further comprising an annular bumper carried by the roof and projecting radially outwardly therefrom below the casing and toward the tank side wall, thereby to protect the casing against undue collapse of any segment thereof incident to sidewise movement of the adjacent segment of the roof wall structure toward the tank side wall.

Further features of the invention pertain to the particular arrangement of the elements of the sealing mechanism,

3,307,733 Patented Mar. 7, 1967 whereby the above-outlined and additional operating features thereof are attained.

The invention, both as to its organization and method of operation, together with further objects and advantages thereof, will best be understood by reference to the following specification, taken. in connection with the accompanying drawings, in which:

FIGURE 1 is a top perspective view, partly broken away, of a tank for storing liquids, such as petroleum products, and provided with a floating roof carrying sealing mechanism embodying the present invention;

FIG. 2 is an enlarged fragmentary top perspective view of a portion of the side wall of the storage tank and an adjacent portion of the floating roof carrying the sealing mechanism mentioned, this view being taken generally in the direction of the arows along the line 2-2 in FIG.

FIG. 3 is an enlarged vertical sectional view of the sealing mechanism, as shown in FIG. 2;

FIG. 4 is an enlanged horizontal sectional view of the sealing mechanism, this view being taken in the direction of the arrows along the line 4-4 in FIG. 3; and

FIG. 5 is a reduced diagrammatic circumferential development of the arrangement of the stays that are incorporated in the sealing mechanism.

Referring now to FIGS. 1 and 2 of the drawings, there is illustrated a tank 10 for storing liquids, such as petroleum products, that includes an upstanding substantially cylindrical side wall 11 and provided with an open top bounded by an annular rim 12 and carrying an annular windgirder 13 arranged about the upper outer portion thereof and adjacent to and below the annular rim 12. Also, an annular roof 20 of piston-like construction is arranged in the tank 10 in floating relation with the stored liquid, indicated at 14; whereby the floating roof 20 rises and falls with respect to the side wall 11 of the tank 10 in accordance with the head of the body of liquid 14 stored therein. As illustrated, the floating roof 20 comprises inner structure defining a centrally disposed annular pontoon 21, outer structure defining an outer annular pontoon 22, and connecting structure defining an annular deck 23. As best shown in FIG. 2, the outer annular pontoon 22 comprises an upper annular plate 24, a lower annular plate 25, an outer upstanding annular rim: 26, and an inner upstanding annular rim, not shown; wherein the outer annular rim 26, disposed in upstanding position, is spaced radially inwardly from the tank side wall 11 to define an annular space 27 therebetween.

As best shown in FIGS. 2 and 3, the outer annular rim 26 of the outer annular pontoon 22 carries sealing mechanism 30 embodying the features of the present invention and essentially comprising a substantially annular tubular casing 31 arranged in the annular space 27 and located principally above the level, indicated at 14a, of the stored liquid 14. An annular body 32 of self-supporting resilient material of cellular structure is enclosed by the casing 31; and the body 32 substantially completely fills the casing 31; whereby the casing 31 constitutes an outer wrapper for the body 32. The casing 31 is attached to the top of the annular rim 26, so that the casing 31 and the body 32 enclosed thereby are movable with the floating roof 20 and relative to the tank side wall 11. The casing 31 is formed of flexible non-metallic sheet-like material that is impervious to the constituents of petroleum products and to water and to air.

Preferably, the body 32 has a radial or lateral crosssection that is of substantially octagon-shape; and the body 32 is arranged in the annular space 27 so that two opposed upstanding faces thereof are respectively pre sented to the annular rim 26 and to the tank side wall 11 and so that two other opposed faces thereof are respectively disposed in top and bottom positions. Thus, the

casing 31 comprises an inner side wall or run 31a lying along the outer surface of the annular rim 26, an outer side wall or run 31b lying along the inner surface of the tank side wall 11, a bottom wall or run 310 submerged in the liquid 14 and connecting the lower portion of the inner and outer side walls 31a and 31b, and a top wall or run 31d positioned above the liquid level 14a and adjacent to the upper portion of the annular space 27 and extending between the upper portions of the inner and outer side walls 31a and 31b. The body 32 extends between the inner and outer side walls 31a and 31b and constitutes a resilient cushion urging the inner side Wall 31a into firm sealed relation with the annular rim 26 and urging the outer side Wall 3112 into firm sealed relation with the tank side wall 11 during both vertical movements and sidewise movements of the roof 20 with respect to the tank side wall 11.

The securing of the sealing mechanism 30 onto the annular rim 26 is effected by an upstanding clamping ring 41, a plurality of arcuate-shaped clamping bars 42, a plurality of clamping washers 43, a plurality of threaded studs 44, and a plurality of nuts 45; and the sealing mechanism 30 is retained in proper position upon the annular rim 26 by a plurality of stays 33. Each ofthe stays 33 has a generally T-shape, including a strap-like stem 34 and a red-like head 35. More particularly, the clamping ring 41 is arranged in upstanding position and in surrounding relation with the top of the annular rim 26 and is rigidly secured thereto, as by welding, the clamping ring 41 being located somewhat below the top of the annular rim 26, as shown in FIG. 3. The clamping ring 41 carries the studs 44 arranged in circumferentially spaced-apart relation and projecting radially outwardly from the clamping ring 41 and toward the tank side wall 11. The extreme top edge 31ax of the inner wall 31a overlies the clamping ring 41, and the studs 44 project through corresponding circumferentially spaced-apart holes formed therein. The stays 33 are arranged in circumferentially spaced-apart relation, as illustrated in FIG. 5, and disposed in inverted position. The upper end of the strap 34 of each stay 33 has a hole formed therein that receives a corresponding one of the studs 44; and the stays 33 are arranged in overlying relation with respect to extreme top edge Slam of the inner wall 31a, as clearly shown in FIG. 4. The extreme top edge 31032: of the top wall 31d overlies the extreme top edge 31ax of the inner wall 31a and also overlies the straps 34 of the stays 33, and the studs 44 project through corresponding circumferentially spaced-apart holes formed in the extreme top edge 31dx of the top wall 310.. The clamping bars 42 are arranged in circumferentially spaced-apart relation and are disposed in overlying relation with the extreme upper edge 31dx of the top wall 31d. Similarly, the clamping washers 43 are arranged in circumferentially spaced-apart relation and are disposed in overlying relation with the extreme upper edge 31dx of the top wall 31d. The clamping bars 42 and the clamping washers 43 are disposed in alternate positions circumferentially about the clamping ring 41, as clearly shown in FIG. 4.

Thus, the straps 34 of the stays 33 are secured to the clamping ring 41 and project downwardly between the extreme upper edges 31ax and 31dx and into the casing 31 and between the outer surface of the inner wall 31a and the inner face of the body 32; and the heads 35 of the stays 33 are located adjacent to the junction between the lower portions of the inner wall 31a and the inner portion of the bottom wall 310. The stays 33 may be spaced apart by a distance S (about 3 feet), as shown in FIG. and the spacing D, as shown in FIG. 5, between the adjacent ends of each pair of heads 35 may be in the general range 3 to 6 inches. This arrangement of the stays 33 positively prevents the casing 31 and the enclosed body 32 from riding-up the tank side wall 11 and out of the annular space 27 incident to downward movement of the floating roof 20 with respect to the tank side wall 11.

The body 32 is preferably arranged in some compression between the side walls 31a and 31b of the casing 31, so that the sealing mechanism 30 effects sealing of the annular rim 26 to the tank side wall 11, notwithstanding substantial sidewise movement of the floating roof 20 with respect to the tank side wall 11; and in order to control this sidewise movement of the floating roof 20, a plurality of circumferentially spaced-apart and radially outwardly projecting bumper elements 28 are carried by the lower plate 25 of the outer pontoon 22, as best shown in FIG. 3. The bumper elements 28 project radially outwardly below the bottom wall 310 of the casing 31 and toward the tank side wall 11 a suitable distance, so as to limit the sidewise movement of the floating roof 20 toward the tank side wall 11, and so as to prevent undue compression or crushing of the body 32 between the annular rim 26 and the tank side wall 11 incident to such sidewise movement of the floating roof 20 toward the tank side wall 11.

Again referring to FIGS. 1 and 2, the top of the annular rim 26 carries a weather hood 50 that may comprise a plurality of individual sections 51 and that may be of the construction and arrangement of that disclosed in U.S. Patent No. 2,997,200, granted on August 22, 1961, to Anthony P. Giannini and Eli F. Smith. The weather hood 50 projects upwardly and outwardly from the top of the annular rim 26 and over the top of the annular space 27 and thus over the sealing mechanism 30 and into engagement with the interior surface of the tank side wall 11; whereby the weather hood 50 protects the sealing mechanism 30 from the elements of weather and prevents entry of such elements through the annular space 27 and thus into the interior of the tank 10.

As indicated in FIG. 3 an annular air pocket 36 is formed within the casing 31 adjacent to the junction of the upper portion of the inner wall 31a and the inner portion of the top wall 31d and at the corresponding face of the body 32 disposed between the two walls 31a and 3111; which air pocket 36 communicates with the atmosphere via a great plurality of pairs of passages 37 respectively formed on opposite sides of the straps 34 of the stays 33, as best shown in FIG. 4. This arrangement accommodates breathing between the interior of the casing 31 and the exterior incident to sidewise movements of the annular rim 26 toward and away from the tank side wall 11, as the body 32 is correspondingly compressed and expanded.

In the sealing mechanism 30, the casing 31 may comprise a flexible sheet including a buna-N vinyl synthetic organic resin coated on a reinforcing fabric formed of a polyamide synthetic organic resin, the preferred polyamide resin being nylon. The buna-N vinyl resin comprises a rubber-like material and is substantially superior to natural rubber for the present purpose by virtue of the required characteristics in the presence of petroleum products. Moreover, this material is highly wear-resistant, so that the same is not scuffed or cut, notwithstanding rough seams and welded joints in the tank side wall Ill; whereby the casing 31 is characterized by long life in use. Another suitable material for forming the casing 31 is a polyurethane synthetic organic resin applied on a nylon reinforcing fabric. The polyurethane resin also comprises a rubber-like material, having the general appearance of foamed rubber. Specifically, this resinous composition is of tough cellular construction of the closed cell type, and is substantially superior to natural rubber for the present purpose by virtue of the required characteristics in the presence of petroleum products. Moreover, this material is also highly wear-resistant, so that the same is not scuffed or cut, nothwithstanding rough seams and welded joints in the tank side wall 11; whereby the casing 31 made of this material is also characterized by long life in use. In those installations wherein mildly corrosive chemicals and aromatic hydrocarbon materials such as benzene, toluene, xylene, and the like, are to be encountered, it is preferred that the casing 31 be formed of a flexible sheet essentially comprising a synthetic organic resin that is a copolymer of hexafluoropropylene and vinylidene fluoride such as that sold under the trademark Viton coated on a reinforcing fabric formed of polyester synthetic organic resin such as that sold under the trademark Dacron. The copolymer resin is a rubber-like material and is substantially superior to natural rubber particularly when used in an environment wherein there may be encountered mildly corrosive chemicals and aromatic hydrocarbons. Moreover, this material is likewise highly wearresistant, so that the same is not scufled or cut, withstanding rough seams and welded joints on the tank side wall 11; whereby the casing 31 formed of this material is likewise characterized by long life in use.

Also, in the sealing mechanism 30, the body 32 of resilient cellular material may be formed of foamed polyurethane of the open-cell type; whereby the body 32 is porous and thus communicates with the air in the pocket 36 so as to insure the desired spring-like cushioning characteristic of this resilient material. Such polyurethane may be of the polyether type having a weight of about 1.2 pounds per cubic foot and of open-cell construction so that the body 32 constitutes a very soft cushion; whereby the body 32 maintains the outer side wall 31b of the casing 31 in firm sliding sealed relation with the tank side wall 11, notwithstanding both vertical and radial movements of the annular rim 26 relative to the tank side wall 11..

Further, in conjunction with the construction of the stays 33 it is noted that the straps 34 thereof are formed of leaf spring steel, so that the heads 35 resiliently urge the lower portion of the inner wall 31a radially inwardly into firm sealed engagement with the outer surface of the annular rim 26. Also, the heads 35 serve to hold-down the junction between the walls 31a and 31c of the casing 31, as clearly shown in FIG. 3, thereby to prevent the sealing mechanism 30 from riding-out of the annular space 27.

It will be understood that the weather hood 50 may 'be installed upon the annular rim 26 incident to the installation of the sealing mechanism 30 thereupon, when a new floating roof 20 is built for the storage tank 10. On the other hand, either the sealing mechanism 30, or the weather hood 50, may be independently installed upon a new floating roof 20, or upon an old floating roof 20 incident to repair thereof. not only seals the annular space 27 between the tank side wall 11 and the annular rim 26 of the floating roof 20, but it also serves to bias the floating roof 20 into a radial centered position with respect to the tank side wall 11. Also, the sealing mechanism 30 performs its sealing function, nothwithstanding the vertical and sidewise movements of the floating roof 20 with respect to the tank side wall 11. The weather hood 50 protects the annular space 27 against the entry thereinto of the elements of weather, notwithstanding the vertical and sidewise movements of the floating roof 20 with respect to the tank side wall 11, thereby to render such protection to the sealing mechanism 30 disposed below the weather hood 50.

Preferably, the body 32 comprises a 'series of sections, each about 6 feet long, arranged in end-to-end relation within the casing 31; and in the construction of the sealing mechanism 30 it is not necessary to secure together the adjacent sections of the body 32 and it is not necessary to secure the sections of the body 32 to the casing 31. Thus, the sealing mechanism 30 may be readily and easily constructed on the side of the storage tank in a simple manner.

In view of the foregoing considerations, it is apparent that there has been provided in a tank for storing liquids,

The sealing mechanism 30 r such as petroleum products, and including a floating roof, an improved sealing mechanism for the annular space disposed between the upstanding annular side wall of the tank and the upstanding annular rim of the floating roof.

While there has been described what is at present considered to be the preferred embodiment of the invention, it will be understood that various modifications may he made therein, and it is intended to cover in the appended claims all such modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. In a tank for storing liquids, such as petroleum products, including an upstanding substantially cylindri cal side wall, and a floating roof arranged in said tank and including upstanding substantially cylindrical wall structure spaced radially inwardly from said tank side wall and defining a substantially annular space therebetween; sealing mechanism for said annular space comprising a substantially annular tubular casing arranged in said annular space and located principally above the level of the stored liquid, means for attaching said casing to the adjacent portion of said roof wall structure, so that said casing is movable with said roof wall structure and with respect to said tank side wall, said casing being formed of flexible non-metallic sheet-like material that is impervious to the constituents of petroleum products and to water and to air, said casing including an inner side wall lying along the outer surface of said roof wall structure and an outer side wall lying along the inner surface of said tank side wall and a bottom wall connecting the lower portions of said inner and outer side walls and a top wall extending between the upper portions of said inner and outer side walls, an annular body of self-supporting resilient material of cellular structure enclosed by said casing and substantially completely filling the same, whereby said casing constitutes an outer wrapper for said body, said body having a lateral cross section that is substantially octagonal with a first pair of opposed faces respectively engaging said casing inner and outer side walls and with a second pair of opposed faces respectively engaging said casing bottom and top walls, whereby said body constitutes a resilient cushion urging said casing inner side wall into firm sealed relation with said roof wall structure and urging said casing outer wall into firm sealed relation with said tank side wall during both vertical movements and sidewise movements of said roof wall structure with respect to said tankside wall, the material of said casing outer side wall also being highly wear-resistant to prevent undue scuffing thereof in its sliding movements in direct contact and sealed engagement with said tank side wall, a plurality of stays carried by said roof wall structure in an annular array and positioned in circumferentially spaced-apart relation with respect to each other, said stays being secured to the upper portion of said roof wall structure above said casing and projecting downwardly along said roof wall structure and into said casing and between said casing inner side wall and said body so that the upper portion of said casing inner side wall underlies the upper portions of said stays and the inner portion of said casing top wall overlies the upper portions of said stays, said stays respectively terminating at the lower portions thereof in parts located between said casing and said body and adjacent to the junction between the lower portion of said casing inner side wall and the inner portion of said casing bottom wall, and means including said stays for positively preventing said casing from riding-up said tank side wall and out of said annular space incident to downward movement of said roof wall structure with respect to said tank side wall.

2. The sealing mechanism set forth in claim 1, wherein each of said stays is substantially T-shaped including a stem and a head, each of said stays is secured to said roof Wall structure in inverted position adjacent to the end 7 of the stem thereof and With the head thereof constituting the part thereof that is located Within said casing and adjacent to the junction between the lower portion of said casing inner side Wall and the inner portion of said casing bottom Wall.

References Cited by the Examiner UNITED STATES PATENTS Anderson 22026 Fino 22026 Horner 22026 Reese et a1. 22026 Giannini 22026 Fino 22026 Moyer 220 -26 Ulrn et a1. 22026 Fino 22026 THERON E. CONDON, Primary Examiner.

JAMES T. GARRETT, Examiner. 

1. IN A TANK FOR STORING LIQUIDS, SUCH AS PETROLEUM PRODUCTS, INCLUDING AN UPSTANDING SUBSTANTIALLY CYLINDRICAL SIDE WALL, AND A FLOATING ROOF ARRANGED IN SAID TANK AND INCLUDING UPSTANDING SUBSTANTIALLY CYLINDRICAL WALL STRUCTURE SPACED RADIALLY INWARDLY FROM SAID TANK SIDE WALL AND DEFINING A SUBSTANTIALLY ANNULAR SPACE THEREBETWEEN; SEALING MECHANISM FOR SAID ANNULAR SPACE COMPRISING A SUBSTANTIALLY ANNULAR TUBULAR CASING ARRANGED IN SAID ANNULAR SPACE AND LOCATED PRINCIPALLY ABOVE THE LEVEL OF THE STORED LIQUID, MEANS FOR ATTACHING SAID CASING TO THE ADJACENT PORTION OF SAID ROOF WALL STRUCTURE AND SAID CASING IS MOVABLE WITH SAID ROOF WALL STRUCTURE AND WITH RESPECT TO SAID TANK SIDE WALL, SAID CASING BEING FORMED OF FLEXIBLE NON-METALLIC SHEET-LIKE MATERIAL THAT IS IMPERVIOUS TO THE CONSTITUENTS OF PETROLEUM PRODUCTS AND TO WATER AND TO AIR, SAID CASING INCLUDING AN INNER SIDE WALL LYING ALONG THE OUTER SURFACE OF SAID ROOF WALL STRUCTURE AND AN OUTER SIDE WALL LYING ALONG THE INNER SURFACE OF SAID TANK SIDE WALL AND A BOTTOM WALL CONNECTING THE LOWER PORTIONS OF SAID INNER AND OUTER SIDE WALLS AND A TOP WALL EXTENDING BETWEEN THE UPPER PORTIONS OF SAID INNER AND OUTER SIDE WALLS, AN ANNULAR BODY OF SELF-SUPPORTING RESILIENT MATERIAL OF CELLULAR STRUCTURE ENCLOSED BY SAID CASING AND SUBSTANTIALLY COMPLETELY FILLING THE SAME, WHEREBY SAID CASING CONSTITUTES AN OUTER WRAPPER FOR SAID BODY, SAID BODY HAVING A LATERAL CROSS SECTION THAT IS SUBSTANTIALLY OCTAGONAL WITH A FIRST PAIR OF OPPOSED FACES RESPECTIVELY ENGAGING SAID CASING INNER AND OUTER SIDE WALLS AND WITH A SECOND PAIR OF OPPOSED FACES RESPECTIVELY ENGAGING SAID CASING BOTTOM AND TOP WALLS, WHEREBY SAID BODY CONSTITUTES A RESILIENT CUSHION URGING SAID CASING INNER SIDE WALL INTO FIRM SEALED RELATION WITH SAID ROOF WALL STRUCTURE AND URGING SAID CASING OUTER WALL INTO FIRM SEALED RELATION WITH SAID TANK SIDE WALL DURING BOTH VERTICAL MOVEMENTS AND SIDEWISE MOVEMENTS OF SAID ROOF WALL STRUCTURE WITH RESPECT TO SAID TANK SIDE WALL, THE MATERIAL OF SAID CASING OUTER SIDE WALL ALSO BEING HIGHLY WEAR-RESISTANT TO PREVENT UNDUE SCUFFING THEREOF IN ITS SLIDING MOVEMENTS IN DIRECT CONTACT AND SEALED ENGAGEMENT WITH SAID TANK SIDE WALL, A PLURALITY OF STAYS CARRIED BY SAID ROOF WALL STRUCTURE IN AN ANNULAR ARRAY AND POSITIONED IN CIRCUMFERENTIALLY SPACED-APART RELATION WITH RESPECT TO EACH OTHER, SAID STAYS BEING SECURED TO THE UPPER PORTION OF SAID ROOF WALL STRUCTURE ABOVE SAID CASING AND PROJECTING DOWNWARDLY ALONG SAID ROOF WALL STRUCTURE AND INTO SAID CASING AND BETWEEN SAID CASING INNER SIDE WALL AND SAID BODY SO THAT THE UPPER PORTION OF SAID CASING INNER SIDE WALL UNDERLIES THE UPPER PORTIONS OF SAID STAYS AND THE INNER PORTION OF SAID CASING TOP WALL OVERLIES THE UPPER PORTIONS OF SAID STAYS, SAID STAYS RESPECTIVELY TERMINATING AT THE LOWER PORTIONS THEREOF IN PARTS LOCATED BETWEEN SAID CASING AND SAID BODY AND ADJACENT TO THE JUNCTION BETWEEN THE LOWER PORTION OF SAID CASING INNER SIDE WALL AND THE INER PORTION OF SAID CASING BOTTOM WALL, AND MEANS INCLUDING SAID STAYS FOR POSITIVELY PREVENTING SAID CASING FROM RIDING-UP SAID TANK SIDE WALL AND OUT OF SAID ANNULAR SPACE INCIDENT TO DOWNWARD MOVEMENT OF SAID ROOF WALL STRUCTURE WITH RESPECT TO SAID TANK SIDE WALL. 